The present invention relates to a fastener system for multi-piece swage type threaded fasteners and an installation tool for installing such fasteners, and having a compact structure adaptable for use in applications with restricted clearance.
The present invention is related to fastener systems and installation tools as shown and described in U.S. Pat. No. 5,315,755 issued May 31, 1994, U.S. Pat. No. 5,548,889 issued Aug. 27, 1996 and U.S. Pat. No. 5,604,968 issued Feb. 25, 1997 all to D. Fulbright et al.
Swage type fasteners are frequently of a two-piece construction comprising a pin and a collar adapted to be swaged into locking grooves on the pin. Conventional swage type fasteners are shown in U.S. Pat. Nos. 2,531,048 and 2,531,049 to L. Huck both issued on Nov. 21, 1950 and are pull type swage fasteners. In the typical pull type fastener, the pin is provided with an enlarged head and a pin shank having locking grooves in a lock groove portion; the pin shank terminates in an elongated pintail portion constructed with pull grooves adapted to be gripped by a jaw assembly of an installation tool. A swage anvil is provided on the tool to engage and swage the collar into the locking grooves. A relative axial force is applied between the pin and collar, and hence between workpieces to be fastened together, as the tool pulls on the pin via the pintail portion with the force being reacted by the engagement of the swage anvil with the collar. This relative axial force pulls the workpieces together under an initial clamp load.
As the relative axial load increases the swage anvil moves axially to radially overengage the collar, swaging it into the locking grooves, whereby the pin and collar are locked together and the final clamp load on the workpieces is developed.
Typically the pintail portion is connected to the locking groove portion by a breakneck groove which is constructed to break at a preselected axial load after the swaging step has been completed whereby the pintail portion is severed and discarded.
In the stump type version, the lockbolt is set by a squeeze type tool which has a stationary member at one end of the workpieces for engaging the pin head and a swage anvil at the opposite end for engaging the collar. The fastener is set as the anvil moves axially against and radially over the collar with the axial force being reacted by the engagement of the stationary member with the pin head. Thus the stump type fastener has the advantage of a shorter pin shank since the pintail portion with pull grooves and breakneck groove is not required. Because of the latter the stump version has the advantage of being lighter and of a lower cost.
But there are other advantages of the stump type swage fastener relative to the pull type fastener. With the pull type fastener, the severed pintail portion creates debris in the work area requiring periodic collection and disposal. Also the stump version will assure a smooth, finished end at the pin shank whereas the pull type pin shank will occasionally have a rough surface from the break at the breakneck groove. Finally the noise occasioned by pin break is absent in the stump type fastener.
There are, however, numerous applications in which a stump type fastener cannot be used or it is not expedient to do so. One example is an assembly in which there is insufficient clearance on the pin head side of the workpieces to permit access for the related stationary portion of the squeeze tool. A similar example for a pull type fastener is an assembly having insufficient clearance to permit insertion of the longer pull type pin into the mating openings of the workpieces and engagement by the installation tool. The present invention addresses such problems. Thus with the present invention a unique fastening system including a swage type fastener and installation tool is provided for a pull type installation but, as will be seen, having advantages of a stump type fastener and installation. Indeed, where both squeeze type and pull type applications and apparatus are present, the swage type threaded fastener can be installed in either application resulting in a reduction in overall inventory and in the numbers of different parts to be stocked. At the same time the installation tool of the present invention can be used to install the swage type threaded fasteners in close clearance applications and thus provides even greater versatility for use of such fasteners.
The present invention is directed to an installation tool for a swage type threaded fastener, as shown in the above patents to Fulbright et al, with a pin having a shank constructed without a severable pintail portion but terminating in a short, threaded or other grippable, pull portion of minimal length. A unique tool is shown which functions to provide a pull type installation for general use but also with specific use in applications with limited clearance. As with the installation tool of the above patents to Fulbright et al the tool includes a threaded, hardened nut member adapted to threadably engage the short pull portion of the pin via rotation by a rotary drive motor. Once a sufficient number of threads have been engaged or gripped by the nut member, the pull tool is actuated to apply a relative axial force by pulling on the pin, through the nut member, with a swage anvil engaging the collar to react the pulling force. At this juncture, the fastening system performs similarly to a conventional pull type installation system. Thus as the magnitude of the relative axial force increases the workpieces being secured are pulled and clamped together under a desired preload. Upon further increases in the axial force the anvil will be moved axially to radially overengage the collar and swage it radially into the locking grooves on the pin shank providing the final clamp load. Next the direction of relative axial force between the swage anvil and nut member is reversed moving the swage anvil in the opposite axial direction to thereby eject the swaged collar. Finally, the hardened nut member is reverse rotated from the short, threaded pull portion removing the installation tool and completing the installation. A rotary drive motor in the pull tool is used to thread the nut member onto and off from the threaded pull portion.
In the above patents to Fulbright et al pins with numerous forms of pull grooves and lock grooves are shown. In addition various forms of collars are shown, i.e. some with a mating female thread of limited extent, etc. As will be seen the unique installation tool of the present invention can be readily used with any of such constructions.
One such fastener structure utilizes a collar with a limited thread and is shown and described in the U.S. Pat. No. 4,867,625 issued Sep. 19, 1989 to R. Dixon for xe2x80x9cVariable Clamp Fastener and Methodxe2x80x9d. Alternatively, a collar with a flexible tab can be used for fit-up; such a structure is shown in the U.S. Pat. No. 4,813,834 for xe2x80x9cFit-Up Fastener With Flexible Tab-Like Structure and Method of Making Samexe2x80x9d issued Mar. 21, 1989 to Walter J. Smith. Both of such fasteners are sometimes referred to as xe2x80x9cfit-up fastenersxe2x80x9d.
In a preferred form of the invention, the tool nut member is designed simply to threadably engage and thereby grip the minimum length pull portion of the pin; thus, in this first step, the tool nut member is not moved against the collar with any significant force and hence is not used to pull the workpieces together and/or clamp them under an initial preload. After the threaded engagement step, the installation tool is actuated to cause the swage anvil to move axially against the collar in response to a relative axial force applied between the nut member and the anvil. Thus the initial clamp up and preload of the workpieces is substantially provided for the first time by the relative axial force applied between the nut member as engaged with the pull portion of the pin shank and the engagement of the swage anvil with the collar. As previously described, the relative axial force is increased until the swage cavity of the anvil is moved axially to radially overengage the collar swaging the collar material into the pin. With this construction, the rotary drive motor for the nut member simply provides the function of threading the nut member on and off the short pull portion of the pin shank and is not used to apply any significant axial load to the workpieces. Thus the capacity of the drive motor can be small permitting the overall size of the installation tool to be minimized.
As will be seen from the description of the installation tool which follows, various forms of the installation tool can be used for installation of such fasteners in various applications with limited clearance. Indeed it will also be seen that the installation tool of the present invention is of a construction which is readily adaptable for use in applications where limited clearance is not a problem.
Thus it is an object of the present invention to provide a novel fastener system including swage type threaded fasteners having the advantages of a stump type fastener and being installed generally as a pull type fastener with an installation tool of unique design.
It is another object of the present invention to provide a novel fastening system including a unique installation tool for use in setting swage type fasteners.
It is another general object to provide a unique fastening system including a unique installation tool of a compact structure for installing swage type threaded fasteners in limited clearance applications.